The overarching goal of this line of research is to examine the role of the hypothalamic-pituitary-adrenocortical (HPA) system in (1) Attention Regulation and (2) Inhibitory Control, aspects of functioning that are potentially related to emotion regulation, behavior problems, and behavior disorders, particularly ADHD. Cortisol, the hormone produced by the HPA system, is known to affect cognitive functioning, particularly declarative and spatial memory and selective attention. The results of two studies provide evidence suggestive of an association between high cortisol concentrations and poorer Inhibitory Control/Attention Regulation in children. The specific goal of the proposed studies is more closely examine the possible linkages between cortisol and attention/inhibitory control to determine that these relations exist before embarking on more expensive, time-consuming longitudinal research. To this end, three studies are proposed, all of which take advantage of existing data sets and "add" either the cortisol measures or the behavior measures. Study 1 uses cortisol measures and Rothbart CBQ (temperament questionnaire) measures already being collected on nursery school children and "adds" observational tests of attention/inhibitory control. Study 2 uses behavioral measures of inhibitory control collected as part of an ongoing longitudinal study (ages 2, 4, and 6) and "adds" measures of cortisol at age 6 years. While Study 3 uses cognitive neuroscience measures of selective attention and executive function being collected to determine norms in 4 to 8 year olds and "adds" cortisol and the Rothbart CBQ temperament questionnaire measures. Studies 2 and 3 are collaborative studies with the investigators responsible for the primary data sets: Grazyna Kochanska (Study 2) and Charles A. Nelson/Monica Luciana (Study 3).